PARENT SESSION
Monday, August 7, 5:00-6:30 pm
Poster Session 4 - Soil, mycorrhizal, and microbial ecology
Exhibit Hall, Ballroom Level, Cook Convention Center

Soil biochemistry responses after six years of multiple global change manipulations in a California grassland.

Gurwick, Noel^{*,1, 2}, Raab, Theodore², Field, Christopher^{1, 2}, Vitousek, Peter², ¹ Carnegie Institution, Stanford, CA, USA² Stanford University, Stanford, CA, USA

ABSTRACT- Although many global change experiments have investigated ecosystem responses to elevated CO₂, nitrogen deposition, precipitation, and heat, few have manipulated more than two factors simultaneously. All four influence plant and soil microbial activity and hence the cycling and storage of carbon and nitrogen in terrestrial ecosystems. To elucidate changes in the fate of C and N in response to global change, and the mechanisms regulating soil C and N pools, we investigated soil chemistry in a multi-factor global change experiment in a California grassland at Jasper Ridge (the JRGCE). To measure bond characteristics in bulk soils and density-separated soil fractions, we employed differential scanning calorimetry (DSC), infrared spectroscopy, and XRay photoelectron spectroscopy (XPS); we also measured IR absorbance and protein content of soil extracts. We found differences among soil free light (FLF) and occluded light (OLF) fractions, and apparent root litter. In particular, OLF appears to have a unique pool of relatively small molecules and a larger lipid pool compared with FLF. XPS analyses also suggested differences in the reactivity of C bonds among density fractions. In N-amended plots subject to elevated CO₂, heat, and precipitation, N resided in complex, thermally-stable molecules absent from plots receiving N amendments only; the fate of N in soil appears to vary depending upon the presence of other global change factors. Existing biogeochemistry models generally do not incorporate soil C and N dynamics directly associated with these chemical differences; our data from the JRGCE provide a starting point for understanding whether they should.

Key words: soil organic matter stabilization, decomposition, thermal decomposition